When performing an operation of, for example, pushing a certain object by a legged mobile robot, such as a bipedal mobile robot, the robot is subjected not only to a floor reaction force from a floor with which a distal portion of a leg thereof is in contact but also to a reaction force from the object. A force other than a floor reaction force that is applied to the robot from an external environment will be referred to as an external force in the present description. In particular, an external force (reaction force) that the robot receives from the object will be referred to as an object reaction force. Incidentally, an external force does not include gravitational force.
As a technology for generating a gait of a robot or controlling an operation thereof in a state wherein an external force is acting on a legged mobile robot, there has been known a technology disclosed in, for example, Japanese Patent Application Laid-Open Publication No. H10-230485 by the present applicant (hereinafter referred to as Patent Document 1). According to the technology, a desired gait is generated such that a dynamic balance condition that a component (horizontal component), excluding a vertical component, of a moment produced about a desired ZMP (a desired floor reaction force central point) by a resultant force of an inertial force produced due to a motion of a robot and the gravity and an external force acting on the robot is zero (a floor reaction force acting on the desired floor reaction force central point and the aforesaid resultant force are balanced with each other) is satisfied. Furthermore, according to the technology, even if an external force acting on the robot turns into an unexpected external force (even if a difference between a desired external force and an actual external force increases to a certain extent), a desired gait of the robot is adjusted such that a position of the center-of-gravity of the robot is balanced to a position of the center-of-gravity that makes it possible to maintain the dynamic balance of the robot.
Meanwhile, as a technology for generating a desired gait of a robot in real time, there has been also known a technology disclosed in PCT international laid-open publication WO/02/40224A1 (hereinafter referred to as “Patent Document 2”) previously proposed by the present applicant. According to the technology, a desired gait of a robot is generated in real time by generating the desired gait such that body position/posture of the desired gait are converged to body position/posture of a normal turning gait, which is a virtual cyclic gait, while securing continual stability of the robot (while preventing a motion state of the robot from diverging).
According to the technology disclosed in Patent Document 1 described above, a basic desired gait is simply generated such that the aforesaid dynamic balance condition is satisfied. Hence, there are cases where a basic desired gait considerably deviates from a gait that satisfies an original dynamic balance condition in response to an unexpected external change. And, in such a case, even if the body position/posture of the robot are adjusted to balance a position of the center-of-gravity, the dynamic balance of the robot cannot be immediately secured, leading to a danger that a continuous motion of the robot cannot be stably accomplished. Further, if a sudden change in an external force takes place in, for example, a case where an operation for moving an object is started by causing an arm or the like of the robot to come in contact with an object from a state wherein the robot is still not in contact with the object, there has been also a danger that a continuous motion of the robot cannot be stably accomplished, as described above.
Further, according to the technology shown in Patent Document 2, no external force is taken into account, making it impossible to generate a desired gait that allows continual stability of a robot to be secured in an environment wherein an external force acts on the robot.
The present invention has been made in view of the background described above, and it is an object of the invention to provide a gait generating system and a control device that make it possible to generate a desired gait that allows continual stability of a robot to be secured even if an external force suddenly changes in an environment wherein an external force is applied to the robot as necessary, such as a reaction force acting on the robot from a certain object when the object is moved by the robot. Further, it is another object of the invention to provide a gait generating system and a control device that make it possible to generate a desired gait that allows continual stability of a robot to be secured even if the external force is not necessarily as expected.